A femtometer (fm) is a unit of length equal to one quadrillionth of a meter:

1 fm = 10-15 m = 1e-15 m

When I use Google Search's built-in unit conversion to calculate 3 femtometers, instead of returning the expected 3e-15 it returns 1,856e+20*
* Comma is decimal separator in my locale
What's up with this?

Google screenshot. Search query: "3 fm in m". Result: "Length: 3 Femtometre = 1,856e+20 Meter." Formula: "for an approximate result, multiply the length value by 6,188e+19"


1 Answer 1


Appears to be a Bug


  1. Femtometre is not listed by default in Google's 'unit conversion' length list but is added as a result of the actual search.
  2. Note the spelling variation between femtometre and meter which is peculiar as I would expect both to follow the same localization rules.
  3. When I trigger the alternative "femtometer" spelling in 'unit conversion' (in my locale), the conversion becomes accurate.
  4. I can only trigger the alternative spelling (accurate unit conversion) in the following way:
    1. Using the full unit name "femtometer" (either spelling) without specifying any quantity. For example, all of the following will work:

      m to femtometer        m to femtometre  
      meter to femtometer    meter to femtometre
      metre to femtometer    metre to femtometre
      femtometer to m        femtometre to m  
      femtometer to meter    femtometre to meter
      femtometer to metre    femtometre to metre
    2. Specifying a 'from' quantity as long as the unit conversion is to, not from, the full unit name femtometer(s), with either spelling:

      3 m to femtometer      3 m to femtometre  
      3 meter to femtometer  3 meter to femtometre
      3 metre to femtometer  3 metre to femtometre
    3. Specifying a 'to' quantity as long as the unit conversion is to, not from, the full unit name femtometre(s), and the US spelling is not used:

      m to 3 femtometre  
      meter to 3 femtometre
      metre to 3 femtometre

      Google Search: "meter to 3 fentometre" Length: "3 Femtometer = 3e-15 Meter" Formula: "for an approximate result, divide the length value by 1e+15"

Reporting Incorrect Answers

At the bottom of the Google Search Help page, Manage calculator, unit converter & color codes, under Send feedback, it indicates you should send feedback to Google if you get an incorrect answer.

  1. At the top right of the page, click Settings Settingsand thenSend feedback.
  2. Enter your feedback.
  3. Select Send

   settings button at the top right of the Google Search page

   Send feedback form filled out with a description of the problem, a screenshot of the search results showing the , error and a checkbox selected that reads "We may email you for more information or updates"

   Report sent, thank you! We use feedback like yours to help fix issues and improve Google services. Close button

  • 1
    When I do the search meter to 3 femtometer (using my native—American—spelling), it says "for an approximate result, multiply the length value by 6.188e+19" and returns a result according to this incorrect formula ("1.856e+20"). For some reason, it's using the British spelling "femtometre" in the dropdown. The Chrome browser omnibox returns the correct answer without doing a search, however.
    – Laurel
    Commented Jan 11 at 21:13

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